The present invention relates to a device for printing and assembling a plurality of ceramic sheets used to manufacture multilayer ceramic capacitors, and more particularly, to a printing device including an octagonal drum rotatable about a horizontal axis which functions as a transport mechanism to conduct ceramic sheets to the several stations at cardinal points arranged around the axis of rotation of the drum at which various process phases are performed.
Among the several known methods for producing multilayer capacitors is the method described in commonly owned U.S. Pat. No. 4,353,957. A plurality of thin leaves of finely divided ceramic composition are made by the use of a thermally-fugitive bonding material, for example, a resin or cellulose derivative, the ceramic composition being such as to form a dense dielectric layer when sintered. There is then applied to each of the leaves a matrix of images by applying a thin layer of what is commonly known in the art as "ink", a liquid or pasty composition which consists principally of a finely dispersed metal powder in a polymeric fluid. The images are produced by depositing the ink on the ceramic leaves, for example, by painting or screen printing procedures which are themselves well known to those skilled in the art.
The screened layers are smaller in surface area than the thin leaves to which they are applied, and each layer is of such a shape as to allow a margin of the associated leaf to extend around a major portion of the perimeter of the screened layer, while a portion of the latter extends to an edge of the leaf on which it is deposited. Preferably, the layers are equal in size.
A plurality of the leaves of the bonded ceramic composition are then stacked, with layers of ink intervening, and consolidated. The consolidation can be accomplished by means suitable to the particular materials employed, and may involve pressing, heating and/or the use of a solvent, all of which also are known to those skilled in the art. The leaves and intervening layers in the stack are so arranged that successive layers extend to different edge regions of the consolidated stack, but a major portion of the edges of each of the leaves is in contact with the edges of the adjacent leaves in the stack. The consolidated stack of leaves and intervening screened layers is then fired to remove the thermally-fugitive materials and to sinter the ceramic composition. There is thereby formed an integral, sintered, ceramic body having a plurality of thin sheets or strata of dense dielectric material, the sheets being joined at portions of their edges but being separated from one another over substantial portions of their adjacent surfaces and having between them thin cavities interrupted only by one or more distinct ceramic and/or metal pillars, substantially all of which, when there are a plurality, are separate.
Heretofore, the various phases in the manufacture of such multilayer ceramic capacitors, such as loading the ceramic leaves into a printing or screening mechanism, printing a layer of ink on the leaves, and stacking the plurality of inked leaves prior to consolidation, have been carried out at least in part manually and in part by several different apparatus. The obvious disadvantages of the known methods include the relatively large commitments of labor and of work space to accommodate the several apparatus, along with defective end products due to human and/or mechanical inaccuracies.
Accordingly, it is among the objects of the present invention to simplify the manufacture of multilayer ceramic capacitors by combining in a single apparatus operable by one person means for performing several of the process phases of their manufacture, thereby contributing to the simplification of the overall operation, minimizing the spatial requirements for apparatus, and reducing inaccuracies and defects in end product.